Toni Morrison never discloses the answer to this question. Part of the point of her story is to experiment with this very question.
Toni Morrison (in her Preface to Playing in the Dark: Whiteness and the Literary Imagination) wrote, "'Recitatif' was an experiment in the removal of all racial codes from a narrative about two characters of different races for whom racial identity is crucial."
By failing to reveal this information to her readers, she asks her readers to consider why race is so important to readers and what a focus on race obscures. For example, if readers stop focusing on race, they might focus on class, disability, gender, or storytelling issues like narration, memory, or trauma.